Ultraviolet radiation (UV)-curable compositions are used as printing varnishes, inks, adhesives for laminates, and in the production of coatings, varnishes and paints for the protection and decoration of a variety of substrates. UV-curable compositions offer significant advantages over typical heat curable compositions. For example, the heat curable compositions contain solvents, and therefore film formation by drying results in environmental pollution. In contrast, UV-curable compositions contain a reactive monomer in place of the solvent. Polymerization of the composition results in the formation of a cross-linked film over the substrate, and thus emission problems are eliminated by the UV-curable compositions.
UV-curable compositions also suffer from certain disadvantages. The compositions generally contain a liquid reactive monomer carrier, free radical initiators to initiate cross-linking of the composition upon UV irradiation, and additives suitable for the intended technical application of the composition. Additives are typically dispersed into the liquid monomer carrier by grinding the additives into a fine powder and mixing the powder into the monomer. This process is associated with numerous problems, including the inhalation hazard involved in handling the finely ground dry powder. Further, the dispersions resulting from this process are nonuniform due to the incompatibility of the additives with the monomer. The nonuniform nature of the dispersion may necessitate the use of surfactants, which in turn results in foaming problems. In particular, foaming causes pinholes in the final cured coating.
An additional disadvantage of the typical process for preparing UV-curable compositions is the lack of stability of the resulting dispersions. The suspended solids may fall out of the liquid monomer after only one or two days. To reduce this tendency, the dispersions are often formulated with higher viscosity, but higher viscosity dispersions are less flowable when incorporated into coatings. Yet another disadvantage of the typical dispersions is a reduction in gloss and clarity in finished surfaces incorporating the dispersions for clear coating applications.
Accordingly, there exists a need in the art for improved methods of producing UV-curable compositions. The present invention provides, inter alia, a method for producing UV-curable compositions that avoids the problems associated with fine dry powders and surfactants, and produces a fine, uniform, and stable product.